The present invention concerns a cooling conduit. It applies in particular, but not exclusively, to the cooling of the batteries of electric or hybrid motor vehicles.
In the present context of consensus about climate change, the reduction in carbon dioxide (CO2) emissions is a major challenge facing motor vehicle manufacturers, as standards are becoming ever more stringent in this field.
In addition to the constant improvement in the efficiency of conventional internal combustion engines, which is accompanied by a fall in CO2 emissions, electric vehicles (EV) and hybrid electric vehicles (HEV) are today regarded as the most promising solution for reducing CO2 emissions.
Various technologies for electrical energy storage have been tested in recent years in order to meet the needs of EVs. It appears today that lithium-ion (Li-ion) cell batteries achieve the best compromise between power density, which promotes performance in terms of acceleration in particular, and energy density, which promotes autonomy. However, this Li-ion technology cannot be used to create traction batteries for EVs without numerous difficulties, in particular if we consider the voltage levels necessary, of the order of 400 Volts (V), and the temperature levels produced. In fact, the migration of lithium ions between the electrodes of an Li-ion cell, whether on discharge when the vehicle is running or on charge when connected to an electrical distribution network, is an exothermic reaction: there is naturally a rise in the cell temperature. But this temperature rise of the cells must nonetheless be controlled since their performance, in particular in terms of power and autonomy, and their useful life depend on the usage conditions, in particular on the operating temperature. The cells, which are furthermore enclosed in a semi-sealed housing normally known as a “pack” or “battery pack”, must therefore be kept within a substantially optimal operating temperature range, both on charging and on discharging. In particular, if the temperature is too high, the cell life will be reduced. This is a problem which the present invention proposes to solve.
One conventional solution is cooling by forced convection as described in patent EP 1031451, for example: the battery pack is situated below the floor of the vehicle and is cooled by a device comprising an inlet conduit for introducing fresh air into the pack, an outlet conduit for evacuating heated air from the pack, and a fan arranged half-way along the outlet conduit to force the circulation of air in the pack by aspiration. One drawback of this solution is that, by forcing the air flow rate in the pack by aspiration, the turbulence phenomena are amplified and disrupt the homogeneity of the air flow rate in the pack. As a direct consequence, the cooling in the pack becomes heterogeneous: as a function of their position in the pack, certain cells are better cooled than others, the air flow rate they receive varying with their location. An indirect consequence is that the performance of the cells varies heterogeneously in the short term, since the performance of a cell in terms of both power and autonomy depends on its temperature. Another indirect consequence is that the life of the cells develops heterogeneously in the long term, as the cells which are not cooled as well age faster. This is a problem which the present invention proposes to solve.
Patent application DE 10 2011 015 337 A1 discloses a method and a device for monitoring the temperature of a battery, which has the same drawbacks linked to the heterogeneity of cooling as patent EP 1031451.